1. Field of the Invention
The present invention relates to an electric connector, and particularly to a multi-pin electrical connector of low insertion force type which permits reduction of the force which is required in inserting its male plug in its female socket.
2. Description of the Prior Art
As is well known, a variety of multi-pin electrical connectors have been proposed and practically used. Such an electrical connector comprises a male plug having a plurality of pin terminals each having a tapering tip, and a female socket having a plurality of contacts each adapted to make a resilient contact with the tapering tip-and-consecutive flat side of a corresponding pin terminal. At an early stage of development all pin terminals have one and same inclination angle at its tapering tip.
FIG. 26 shows the insertion force-to-insertion depth characteristics of a pin terminal when inserted in a counter contact. As seen from the graph, the insertion force rises with the increase of the insertion depth, and it will reach its peak value when the pin terminal comes close to its final contact position, and accordingly the intervening angle between the tapering tip of the pin terminal and the contact surface decreases. When the intervening angle reduces to zero, the insertion force levels off as indicated at F.sub.0. The peak value is indicated at F.sub.1 in the graph, and sometimes the force of the peak value is called "insertion force". Here, it should be noted that all pin terminals in the socket reach their final positions simultaneously, a multiplied.
As a result, the resultant insertion force required for inserting the male plug into the female socket is equal to a multiplication of the insertion force of a single pin terminal by the number of the pin terminals used in the socket. The graph shows the resultant insertion force 2 F.sub.2 of two pin terminals compared with that required for insertion of a single pin terminal into a counter contact.
This shows the multiplied increase of insertion force required in a multi pin electrical connector. There was a strong demand for decreasing the insertion force required in a multi pin electrical connector. In an attempt to meet such a demand a variety of multi pin connectors were proposed, and are actually used. For instance, U.S. Pat. No. 4,679,890 shows a multi pin electrical connector of low insertion force type. It has a plurality of contacts each having a shape symmetrical with respect to its center axis, and a plurality of pin terminals each having different curvatures on its opposite sides with respect to its center axis. This arrangement caused the insertion force of the pin terminal to reach twice at different times because one curvature comes to contact with the counter contact earlier than the other curvature.
This principle may be applied to an electrical connector whose pin terminals are so designed that each pin terminal contacts a counter female contact on its one side. In this case at least two kinds of pin terminals are prepared, and one kind of pin terminal has a first curvature on its contact side whereas the other kind of pin terminal has a second curvature on its contact side. These first and second curvatures are different from each other, hence causing insertion of forces to appear at different times, thereby substantially decreasing the resultant insertion force compared with use of only one kind of tapering pin terminals, which would cause simultaneous increase of insertion forces, requiring a multiplied resultant insertion force.
Pin terminals are punched from a piece of metal plate, and then their tapering tips are trimed to precise desired curvature. To a disadvantage, however, it is very difficult to shape the tapering tip of a pin terminal into a precise curved shape. It is likely that pin terminals have less precise curvatures, and this is a cause for failure in decreasing the resultant insertion force to a desired small value. In other words, the extreme precision is required in making pin terminals of different kinds to attain the satisfactory result.